1. Field of the Invention
This invention relates to a multistage hydraulic machine system including a multistage hydraulic machine having a runner at each of highest- to lowest-pressure stages which communicate by means of a return passage and a mechanism for controlling the operation of the multistage hydraulic machine, and a method for operating the same. (here the multistage hydraulic machine means a multistage-type pump, or pump-turbine.)
2. Description of the Prior Art
In general, operation control for a hydraulic machine may be achieved by adjusting the quantity of water flowing through the hydraulic machine by means of guide vanes arranged around a runner or an inlet valve at an inlet portion of the machine.
Also for the type of multistage hydraulic machine having a runner for each of highest- to lowest-pressure stages which communicate by means of a return passage, there have been designed and proposed various systems for controlling the operation of the machine by controlling water flow at each stage by means of guide vanes arranged around the runner for each stage.
However, in the aforesaid multistage hydraulic machine with such complicated construction wherein the highest- to lowest-pressure stages are successively connected in series by means of the return passage, it is very difficult, from a structural point of view, to perform opening and closing operations by means of an operation mechanism coupled to guide vanes that are arranged round the runner for each stage.
Accordingly, a conventional multistage hydraulic machine is usually so constructed that only fixed guide vanes with fixed opening of water path are arranged around the runner for each stage and that the operation mode may be controlled by opening and closing the inlet valve at the inlet portion of the machine to adjust the quantity of water flow. In such machine, however, it is impossible to properly adjust the flow condition at the outer peripheral portion of the runner in accordance with the flow rate, so that the hydraulic performance of every stage is deteriorated when the flow rate becomes substantially lower or higher than the designed rate, thereby reducing the integrated hydraulic capability of the hydraulic machine in operation. Moreover, if the flow rate is adjusted with the inlet valve moderately closed, the loss of head at the inlet valve portion will increase to nullify water current energy corresponding to such loss, thereby deteriorating the working efficiency of a power plant.